This application is for a 5-year renewal of the Collaborative Genetic Study of Nicotine Dependence. Through a genome wide association and candidate gene study, we successfully identified genes contributing to the development of nicotine dependence, such as the alpha5 nicotinic cholinergic receptor subunit, CHRNA5. The goals of this program are the further identification of genes, environmental features, and biological mechanisms that contribute to the onset and persistence of smoking and nicotine dependence. Project 1 builds upon the foundation laid in the past funding period. This project will use phenotypic refinement and sophisticated genetic modeling to analyze existing data, including the nicotine metabolism endophenotype. The goal of this project is to understand how genes affect the susceptibility to develop nicotine dependence and correlated characteristics. Project 2 will use a combination of genetic and functional approaches to further identify specific risk alleles. We will genotype the most significant SNPs from our previous study in an independent case control series. Genes that show evidence of replication will undergo fine mapping and those with the most compelling evidence of association will be examined in vivo and in vitro to determine functional consequences of the risk alleles. This will shed considerable light on the biological mechanisms underlying nicotine dependence. Project 3 adds a translational component to the program by incorporating mouse genetic models of Chrna5. This will identify and characterize reinforcing and aversive properties of nicotine exposure and basic neurobiological mechanisms through which Chrna5/alpha5 contributes to nicotine addiction. Project 4 examines questions central to understanding smoking cessation and relapse. The follow-up of nicotine dependent cases recruited during the past funding period will be the first longitudinal study of addicted smokers from a community based sample. We will test candidate genes for smoking cessation and relapse;test gene interactions;and test association between candidate genes and endophenotypes involved with cessation and relapse. Our synergistic program project uses a powerful trans-disciplinary approach to suggest novel strategies for reducing tobacco consumption and decreasing the morbidity and mortality that follow.